Brouder, Christian The structure of Green functions in quantum field theory with a general state. (English) Zbl 1159.81389 Fauser, Bertfried (ed.) et al., Quantum field theory. Competitive models. Papers based on the presentations at the workshop on “Recent developments in quantum field theory”, Leipzig, Germany, July 20–22, 2007. Basel: Birkhäuser (ISBN 978-3-7643-8735-8/hbk). 163-175 (2009). Summary: In quantum field theory, the Green function is usually calculated as the expectation value of the time-ordered product of fields over the vacuum. In some cases, especially in degenerate systems, expectation values over general states are required. The corresponding Green functions are essentially more complex than in the vacuum, because they cannot be written in terms of standard Feynman diagrams. Here, a method is proposed to determine the structure of these Green functions and to derive nonperturbative equations for them. The main idea is to transform the cumulants describing correlations into interaction terms.For the entire collection see [Zbl 1153.81002]. Cited in 1 Document MSC: 81T10 Model quantum field theories 81T99 Quantum field theory; related classical field theories 81V70 Many-body theory; quantum Hall effect 82C10 Quantum dynamics and nonequilibrium statistical mechanics (general) Keywords:nonequilibrium quantum field theory; initial correlations; structure of Green functions PDFBibTeX XMLCite \textit{C. Brouder}, in: Quantum field theory. Competitive models. Papers based on the presentations at the workshop on ``Recent developments in quantum field theory'', Leipzig, Germany, July 20--22, 2007. Basel: Birkhäuser. 163--175 (2009; Zbl 1159.81389) Full Text: arXiv